Cell analysis apparatus and method

ABSTRACT

Devices and methods that measure one or more properties of a living cell culture that is contained in liquid media within a vessel, and typically analyzes plural cell cultures contained in plural vessels such as the wells of a multiwell microplate substantially in parallel. The devices incorporate a sensor that remains in equilibrium with, e.g., remains submerged within, the liquid cell media during the performance of a measurement and during addition of one or more cell affecting fluids such as solutions of potential drug compounds.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/486,440 filed Jul. 13, 2006 and issued on Feb. 25, 2014 as U.S. Pat.No. 8,658,349, which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates generally to devices that measure one or moreproperties of a living cell culture that is contained in liquid mediawithin a vessel, and typically analyzes plural cell cultures containedin plural vessels such as the wells of a multiwell microplatesubstantially in parallel. More specifically, the invention relates todevices that incorporate a sensor that remains in equilibrium with,e.g., remains submerged within, the liquid cell media during theperformance of a measurement and during addition of one or more cellaffecting fluids such as solutions of potential drug compounds.

BACKGROUND

Sensor probes may be used to measure a concentration of an analyte in aliquid media surrounding living cells as a means to interrogate thebehavior of the cells and, in particular, to profile behavioral changesthat are induced by exposure of the cells to candidate drug compounds.An example of an apparatus and method for making measurements of thistype is described in U.S. Patent Publication No. 2005/0054028, thedisclosure of which is incorporated by reference herein in its entirety.

One problem that may be encountered in using such a method is that anequilibration period may be required each time that the submersiblesensor probe is placed in or otherwise exposed to the cell media. Theequilibration period may be preferable or required to allow time for theprobe to adjust to the temperature of the media, or for the sensor orits associated electronics to adapt to the difference between ambientair and the cell media. Such equilibration may require seconds, minutes,or hours depending, for example, on the sensor and measurementsensitivity desired.

The equilibration process may be undesirable to the user of theapparatus, because it may lengthen the time needed for analysis, andpotentially may result in a measurement error if sequentialequilibrations have differing characteristics.

A typical reason for removing a sensor probe from the cell media is toallow the addition of a test compound such as a drug candidate. This isparticularly likely when the sensor probe is part of an assemblycontaining an array of probes, and when the test compound is deliveredusing an array of delivery devices such as pipettes, e.g., controlledand implemented by a robot.

SUMMARY OF THE INVENTION

The invention described herein provides a method, apparatus, instrument,cartridge, and measurement system for adding a test compound to avessel, or multiple of the same or different test compounds to multiplewells of a microplate, while a sensor probe remains in equilibrium with,e.g., remains submerged within, the liquid contained within each vesselor well. Because the sensor probe remains submerged during compounddelivery, equilibration time is reduced. Thus, a system and a method areprovided for storing and dispensing a single preselected test compound,or preselected concentration of the compound per vessel or well.Furthermore, the storage and delivery apparatus may be fabricated fromlow cost materials, so that it may be discarded after use to eliminatecross-contamination from one use to another.

In another embodiment, the apparatus and method store and delivermultiple test compounds per well, preferably using a supply ofcompressed gas from a remote source to actuate the compound delivery. Ina preferred embodiment, both the sensor probe and test compound deliverystructure are incorporated within a single disposable cartridge. Apneumatic multiplexer is also described that, when temporarily attachedto the cartridge, allows a single actuator to initiate the delivery oftest compound from multiple ports using a supply of compressed gas froma remote source.

In one aspect, the invention features a cartridge adapted to mate with amultiwell plate having a plurality of wells. The cartridge includes asubstantially planar element having a plurality of regions correspondingto a common number of respective openings of the wells in the multiwellplate. At least one port is formed in the cartridge in at least oneregion, the port being adapted to deliver a test fluid, e.g., an aqueoussolution of a candidate drug compound, to the respective well. Thecartridge also includes at least one of a) a sensor or portion thereofadapted to analyze a constituent in a well and b) an aperture adapted toreceive a sensor located in a sub region of the at least one region ofthe cartridge.

The apparatus and method may include one or more of the followingfeatures. The port forms a capillary aperture to retain test fluid inthe port absent an external force. The external force may be a positivepressure differential force, a negative pressure differential force,and/or a centrifugal force. The sensor (or portion thereof or apertureadapted to receive a sensor) preferably is compliantly attached to theplanar element so as to accommodate slight misalignment of the probestructure with the wells of microplate. A second port is formed in thecartridge in the at least one region, the second port being adapted todeliver a second test fluid to the respective well. The second testfluid may be the same or different from the first test fluid, or adifferent concentration of the previously deposited fluid. The cartridgemay form a cover for the multiwell plate to reduce contamination and/orevaporation of sample in the multiwell plate. Preferably, at least oneport, preferably multiple ports, e.g., four ports, are formed inmultiple regions of the cartridge, and at least one of the sensor andthe aperture adapted to receive the sensor is located in each region.Multiple ports in different regions may be in fluidic communication. Asecond port may be formed in the cartridge in every region. The secondports also may be in fluidic communication with each other and not influidic communication with other ports. A common number of ports may beformed in every region of the cartridge, and a common number of sets ofports. A multiplexer may be in fluidic communication with each set ofports. The multiplexer may be adapted to connect to a single pneumaticsource to permit delivering fluid to the wells sequentially from eachset of ports.

In preferred embodiments, the sensor is adapted to analyze (determinethe presence or concentration of) an extracellular constituent in awell, such as CO₂, O₂, Ca⁺⁺, H⁺, or a consumed or secreted cellularmetabolite. The aperture adapted to receive the sensor may comprise asensor sleeve structure having a surface proximal to a well of themultiwell plate. Disposed on the surface is a fluorophore havingfluorescent properties dependant on at least one of the presence and theconcentration of a constituent in the well. The sensor sleeve mayinclude an elongate housing for receiving a wave guide for at least oneof stimulating the fluorophore and for receiving fluorescent emissionsfrom the fluorophore.

In another aspect, the invention features apparatus comprising a systemfor analyzing cells. The apparatus includes a stage adapted to receiveand position a plate having a plurality of wells and a cartridge whichmates with the multiwell plate. The apparatus also includes an elevatormechanism adapted to move the cartridge relative to the stage or theplate to dispose the sensor in the well, typically multiple sensors inmultiple wells simultaneously. The cartridge comprises a substantiallyplanar element having a plurality of regions corresponding to a numberof respective openings of the wells in the multiwell plate, with eachregion defining at least one port adapted to deliver a test fluid to therespective well. At least one sensor adapted to analyze a constituent ina well is located in each region of the cartridge.

The apparatus may include one or a combination of the followingfeatures: A pressure source adapted to be mated fluidically with thecartridge, to deliver the test fluid from a port in the cartridge to awell; a multiplexer disposed between the pressure source and thecartridge, the multiplexer being adapted to be in fluidic communicationwith a plurality of ports formed in the cartridge. The multiplexer maybe in fluidic communication selectively with exclusive sets of portsformed in the cartridge; a controller to control the elevator mechanism,the multiplexer, and/or the pressure source to enable delivery of testfluid from a given port or set of ports to a corresponding well or setof wells when an associated sensor is disposed in the well.

An array of sensors corresponding to an array of wells may be andpreferably are integral with the cartridge, but may also be separateelements mated with and disposed within apertures formed in thecartridge. The sensor array preferably is mounted compliantly relativeto the well plate. The sensors preferably comprise a fluorophore havingfluorescent properties dependant on at least one of the presence andconcentration of a constituent in the well, and a wave guide forstimulating the fluorophore and for receiving fluorescent emissions fromthe fluorophore.

In another aspect, the invention features a method of analyzing cellsdisposed in media in a multiwell plate. The method includes disposing asleast a portion of a sensor in media in a well in the multiwell plate,analyzing a constituent related to the cells within the media in thewell, delivering a test fluid to the well while the sensor remainsdisposed in the media in the well, and further analyzing the constituentto determine any change therein.

One or more of the following features may be included. The analyzingstep may include analyzing respective constituents related to respectivecells within media in respective wells. The respective constituents maybe the same constituent. The delivering step includes deliveringrespective test fluids to the respective wells while respective sensorsremains disposed within media in respective wells. The respective testfluids may include the same test fluid. The step of analyzing stepincludes analyzing respective constituents related to respective cellswithin media in respective wells to determine any respective changestherein. The delivering step and the further analyzing step may berepeated. A different test fluid or an additional aliquot of the sametest fluid may be delivered between measurements. The method may includesubstantially maintaining equilibration between the sensor and the mediaduring the delivery step or maintaining thermal equilibrium between thetest fluid and the media during the delivery step.

In still another aspect, the invention features an instrument foranalysis of cells disposed in a microplate. The instrument includes astage for positioning a microplate and a plurality of probes, each probepositioned for acquiring data from respective wells in the microplate.The instrument also includes a controller for effecting the addition ofone or more reagents to one or more of the wells of the microplate; anda system in communication with the controller and the probes including agraphical user interface residing on a computer. The graphical userinterface is configured to receive instructions for the design of amulti-well experiment and to receive the data acquired by the probes inresponse to the execution of the multi-well experiment.

One or more of the following features may be included. The instructionsdescribe the addition of one or more selected solutions of potentialcell affecting substances to one or more of the wells. The graphicaluser interface includes a plurality of display areas, each area beingattributed to one of the wells. The display areas include at least oneparameter of the experiment. The display areas include at least oneresult of the experiment, the results being based at least in part onthe data acquired by the probes. The plurality of display areas aredisposed about a screen, the screen representing the microplate. Thedata acquired by the probes in response to the execution of themulti-well experiment includes data spanning multiple microplates, andthe graphical user interface is further configured to display data fromeach microplate on a separate respective screen. The system includes ananalysis engine configured to produce one or more graphicalrepresentations of the data acquired by the probes. The analysis engineis configured to perform statistical analysis on the data acquired bythe probes. The instrument includes a communications module fortransmitting the experiment instructions and the data acquired by theprobes among the controller, the probes and the system. Thecommunication among the controller, the probes and the system is carriedout over a digital communications network. The communications networkincludes a local-area network, a wide-area network, an intranet, theInternet, and/or combinations thereof.

In another aspect, the invention features an instrument for analysis ofreactions of cells disposed in a microplate. The instrument includes astage for positioning a microplate, and a sensor probe positionable foracquiring data from respective wells in the microplate. The instrumentalso includes a system in communication with the probe including agraphical user interface residing on a computer and including aplurality of display areas, each area being attributed to one of thewells. The graphical user interface is configured to receiveinstructions written in respective areas attributed to one of the wellsfor the design of a multi-well experiment, and receive the data acquiredby the sensors in response to the execution of the multi-well experimentfor display in a respective area attributed to one of the wells.

One or more of the following features may be included. The display areasfurther include at least one parameter of the experiment. The displayareas further include at least one result of the experiment, the resultbeing based at least in part on the data acquired by the probes. Theinstrument includes a plurality of the probes. The probe reads at leastone of optical density, luminescence, phosphorescence, and fluorescence.The instrument includes a controller for effecting the addition of atleast one reagent to at least one of the wells, the user interface beingconfigured to receive instructions for the design of a multi-wellexperiment. The instrument includes a single probe addressable to atleast one of a well and a subset of wells. The system includes ananalysis engine configured to produce one or more graphicalrepresentations of the acquired data. The analysis engine is configuredto perform statistical analysis on the acquired data.

The instrument operating software enables the use, by both a desktopapplication and the instrument operating software, of a file thatcontains both experiment design information entered by the user (e.g.,what material is in each well, etc.) and results data entered by theinstrument. An embedded analysis tool may be included. The instrumentoperating software may be incorporated within a third party spreadsheetpackage such as Excel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a complete measurement system andapparatus in accordance with one embodiment of the invention;

FIGS. 2 a and 2 b are upright and inverted (respectively) explodedperspective views of a multiwell plate and a covered cartridge adaptedto mate with the multiwell plate in accordance with one embodiment ofthe invention;

FIGS. 3, 4 and 5 together present a schematic, isolated, partialcross-sectional, exploded view of one region of an embodiment of theapparatus of the present invention, illustrating (FIG. 3) a portion of asensor probe structure including an internal optical fiber bundle forlight transmission to and from fluorescent sensor spots, the probestructures being inserted through a pneumatic multiplexer; the cartridge(FIG. 4—see figures FIGS. 2 a and 2 b) illustrating spots of fluorescentsensors disposed on an outside of a sleeve defining an aperture forreceiving the portion of a sensor probe of FIG. 3, and two ports adaptedto deliver a test fluid to a single well of the multiwell plate; and asingle well of the multiwell plate (FIG. 5, see FIGS. 2 a and 2 b);

FIGS. 6 a and 6 b are schematic cross-sectional views of the probestructure, cartridge portion, and single well of FIGS. 3, 4, and 5 in apartially raised (mix or equilibrate) position and in a lowered (datagathering) position;

FIG. 7 is a schematic top view of four layers of a microfabricatedpneumatic multiplexer, a portion of which is shown in FIG. 3;

FIG. 8 is a schematic cross-sectional view of three regions eachcomprising a probe, a portion of a cartridge, and a well in combinationwith the pneumatic multiplexer of FIG. 7;

FIG. 9 is a schematic view of a sensor probe submerged in the liquidmedia contained within a microplate well;

FIG. 10 is a block diagram of an embodiment of a system according to theinvention;

FIG. 11 is one example of a screen display of one embodiment of thesystem of FIG. 10;

FIG. 12 is another example of a screen display of one embodiment of thesystem of FIG. 10; and

FIG. 13 a, 13 b, 13 c, and 13 d are graphs illustrating the results ofmonitoring metabolic rates in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

The invention enables the measurement of one or more properties ofliving cells that are disposed in, for example, a well of a multiwellmicroplate. Embodiments of the invention include a sensor, preferably asubmersible sensor that enables fast sensor stabilization, therebyincreasing measurement throughput. The disclosed compound storage anddelivery apparatus, pneumatic multiplexer, structure for adding fluidsto subsets or all of multiple wells simultaneously, and sensor structurepermitting non destructive measurement of the effect of addition ofexogenous fluid to respective wells, in combination with the ability tomake and repeat measurements rapidly, results in the provision of a lowcost per test, high throughput cellular assay system ideal, e.g., fordrug discovery applications. Furthermore, the invention provides acartridge structure which permits repeated use of the apparatus fordisparate cellular assays without requiring intermediate cleaning, andwhile eliminating the possibility of cross contamination between tests.Still further, the invention provides software for designing andimplementing multi-well cellular assays run in parallel, and forreceiving and analyzing the generated data that is intuitive and easy touse, permits multiple scientists to design and execute multiwellparallel assays during the same time period, and preferably is based ona spreadsheet program of the type well understood by scientists andeasily integrated with sophisticated LIMS systems.

Referring to FIG. 1, the apparatus 100 is illustrated schematically. Itcomprises a compound storage and delivery apparatus in a housing 105(shown in dashed lines) that includes a cartridge 110 defining aplurality of apertures for receiving sensor structures and a pluralityof fluid ports (shown in detail in FIGS. 2 a and 2 b) compliantlymounted, and a stage or base 130 adapted to receive a multiwell plate120, e.g., a cell culture plate. The cartridge 110 is disposed above,and adapted to mate with, the multiwell plate 120. The cartridge 110optionally is held by a cartridge holder 122 adapted to receive thecartridge 110. The compound storage and delivery apparatus 105 alsoincludes a mounting block 140, which can reciprocate as shown by thedouble headed arrow, preferably powered by a motor (not shown),including an elevator mechanism 145. The elevator mechanism 145 isadapted to move the cartridge 110 relative to the stage 130, or wellplate 120. The mounting block includes a gas multiplexer 150 attached toa pressure source, e.g., gas supply or gas reservoir 160. The gas supply160 is in fluid communication with the cartridge, and is used to impelthe delivery of test fluid from a port in the cartridge to a well in themultiwell plate 120 as disclosed below. A plurality of sensor probes 170are adapted for insertion into the plurality of apertures in thecartridge 110, and may be used to gather data indicative of the state ofcells disposed in wells in the multiwell plate 120.

The compound storage and delivery apparatus 105 is controlled by acontroller 175, that may be integrated with a computer 180, that maycontrol the elevator mechanism, the multiplexer, and the pressuresource. The controller 175 may, thereby, permit delivery of a test fluidfrom a port to a corresponding well when an associated sensor isdisposed in the well.

FIGS. 2 a and 2 b illustrate the currently preferred form of thecartridge 110 and microplate 120, and how they relate to each other Thecartridge is a generally planar element comprising a frame 200 made,e.g., from molded plastics. Planar surface 205 defines a plurality ofregions 210 that correspond to, i.e., register with, a number of therespective openings of a plurality of wells 220 defined in the multiwellplate 120. Within each of these regions 210, in the depicted embodiment,the planar element defines first, second, third, and fourth ports 230,which serve as test compound reservoirs, and a central aperture 215 to asleeve 240. Each of the ports is adapted to hold and to release ondemand a test fluid to the respective well 220 beneath it. The ports 230are sized and positioned so that groups of four ports may be positionedover the wells 220, and test fluid from any one of the four ports may bedelivered to a respective well 220. In other embodiments the number ofports in each region may be less than four or greater than four. Theports 230 and sleeves 240 may be compliantly mounted relative to themicroplate 120 so as to permit it to nest within the microplate byaccommodating lateral movement. The construction of the microplate toinclude compliant regions permits its manufacture to looser tolerances,and permits the cartridge to be used with slightly differentlydimensioned microplates. Compliance can be achieved, for example, byusing an elastomeric polymer to form planar element 205, so as to permitrelative movement between frame 200 and the sleeves and ports in eachregion.

Each of the ports 230 may have a cylindrical, conic or cubic shape, openthrough planar element 200 at the top, and closed at the bottom exceptfor a small hole, i.e., a capillary aperture, typically centered withinthe bottom surface. The capillary aperture is adapted to retain testfluid in the port, e.g., by surface tension, absent an external force,such as a positive pressure differential force, a negative pressuredifferential force, or possibly a centrifugal force. Each port may befabricated from a polymer material that is impervious to test compounds,or from any other solid material. When configured for use with amultiwell microplate 120, the liquid volume contained by each port mayrange from 500 μl to as little as 2 μl, although volumes outside thisrange are contemplated.

In the depicted embodiment, multiwell plate 120 has 24 wells. The numberof wells 220 in a plate may vary from 1 to several thousand. In otherembodiments, a single well of nearly any size may be fabricated, ormultiple wells may be fabricated, or multiple wells may be fabricated ina one- or two-dimensional arrangement. In one embodiment, atwo-dimensional pattern of wells corresponding to the pattern anddimensions of a microplate, as described by the Society for BiomolecularScreening standards for microplates (“SBS-1 Footprints” and “SBS-4 WellPositions,” both full proposed standards updated May 20, 2003), andcontaining a total of 12, 24, 96, 384, 1536, or any other number ofindividual wells may be fabricated.

Referring to FIG. 2 b, in each region of the cartridge 110, disposedbetween and associated with one or more ports 230, is a submersiblesensor sleeve or barrier 240, adapted to be disposed in thecorresponding well 220. Sensor sleeve 240 may have one or more sensors250 disposed on a lower surface 255 thereof for insertion into media ina well 220. One example of a sensor for this purpose is a fluorescentindicator, such as an oxygen-quenched fluorophore, embedded in an oxygenpermeable substance, such as silicone rubber. The fluorophore hasfluorescent properties dependant on the presence and/or concentration ofa constituent in the well 220. Other types of known sensors may be used,such as electrochemical sensors, Clark electrodes, etc. Sensor sleeve240 may define an aperture and an internal volume adapted to receive asensor. Examples of the types of sensors that may be used are describedbelow with reference to FIG. 3.

The cartridge 110 may be attached to the sensor sleeve, or may belocated proximal to the sleeve without attachment, to allow independentmovement. The cartridge 110 may include an array of compound storage anddelivery ports assembled into a single unit and associated with asimilar array of sensor sleeves.

The apparatus may also feature a removable cover 260 for the cartridge110 or for multiwell plate 120. The configuration of cartridge 110 as acover for multiwell plate 120 may help prevent evaporation orcontamination of a sample or media disposed in wells 220. The cover 260may also be configured to fit over the cartridge 110 thereby to reducepossible contamination or evaporation of fluids disposed in the ports230 of the cartridge 110.

Referring also to FIG. 3 through 6 b, details of preferred relationshipof parts is illustrated. FIG. 3 shows a fixed (preferably not part ofthe cartridge and reusable) sensor probe structure 170 configured to fitwithin the sensor sleeve 240. The sensor probe structure 170 includes arigid outer tube 315 made from, e.g., stainless steel. Optical fibers300 are disposed within the tube 315, and are configured to stimulateone or more fluorophores 250 disposed on a light transmissive outsidelower wall portion 325 of sensor sleeve 240 and to receive fluorescentemissions from the fluorophore through the wall portion. When the probeis in its down position, it preferably forms a reduced media test volumein each well, as shown, for example, in FIG. 6 b. As an alternative (notshown) probe sleeve 240 may comprise an annular wall portion extendingbelow portion 325 which defines the reduced test volume. The sensorprobe structure and fluorophore may be configured to read opticaldensity, luminescence, phosphorescence, or, preferably, fluorescence. Inan alternative embodiment (not shown) the sensor probe structure 170 maybe a self contained sensor which gathers data from a well through asignal transmissive bottom wall of the sleeve 240, or directly throughan open bottom on the sleeve, preferably sealed to the probe.

Various types of sensors can be utilized depending on the analysis to beperformed and its selected configuration, including oxygen sensors, suchas oxygen-quenched fluorescent sensors, pH sensors, includingfluorescent sensors, ISFET and impedance sensors using electrodescoupled through bottom wall 325 of sleeve 240, CO₂ sensors, includingbicarbonate buffer coupled and ammonium dye coupled fluorescent sensorsas well as other CO₂ sensors; various ion and small molecule sensors;large molecule sensors including surface plasmon resonance sensors andsensors exploiting the principle of Wood's anomaly; acoustic sensors;and microwave sensors. In certain embodiments, a conventional platereader may be used.

Preferred sensors are fluorophores. Many fluorescent sensing compoundsand preparations are described in the art and many are availablecommercially from, for example, Molecular Probes Inc and FrontierScientific, Inc. The currently preferred oxygen sensor is a fluorophorewith the signal inversely proportional to oxygen concentration such as aporphyrin or rhodamine compounds immobilized as a particle orhomogenously distributed in an oxygen permeable polymer, e.g., siliconerubber. The currently preferred compound is porphyrin. The currentlypreferred pH sensor is a fluorescent indicator dye, fluorescein, whosesignal decreases upon protonation of the dye, and which is eitherentrapped in a particle that is suspended in a carrier polymer, orcovalently attached to a hydrophilic polymer. Useful fluorescent CO2indicator sensor typically are based on a pH sensitive transducer, withthe fluorescence being indirectly modulated by the production ofcarbonic acid due to reaction of carbon dioxide with water. See, e.g. O.S. Wolfbeis, Anal. Chem. 2002, 74, 2663-2678. A fluorophore that detectsglucose also can be used, such as one based on a non-enzymatictransduction using a boronic probe that complexes with glucose,resulting in a charge transfer that modulates the fluorescence of theprobe, or an enzymatic glucose transducer that couples a glucose oxidaseto a fluorescent oxygen sensor, with the binding and oxidation ofglucose resulting in a quantitative modulation of the oxygen sensor. Italso is within the scope of the invention to employ a fluorophore orother type of sensor sensitive to biological molecules such as, forexample, lactate, ammonia, or urea. A lactate sensor can be based on anenzymatic sensor configuration, with lactate oxidase coupled to afluorescent oxygen sensor, and with the binding and oxidation of lactateresulting in a quantitative modulation of the oxygen sensor. An ammoniaor ammonium ion sensor can be configured with immobilization of aprotonated pH indicator in a hydrophobic, gas permeable polymer, withthe fluorescence output quantitatively modulated by reaction withtransient ammonia. A urea sensor can be based on an enzymatic sensorconfiguration, with urease coupled to a fluorescent ammonia transducer,and with the binding and reduction of urea to ammonia, resulting inmodulation of the ammonia sensor fluorescence.

In the illustrated embodiment, the fixed sensor probe 170 is attached toand extends orthogonally from the pneumatic multiplexer 150. Othersensor configurations will be apparent to those skilled in the art. Forexample, probes may be disposed on a wall within the well underexamination, or on a bottom, translucent surface of a well.

Air channels 310 are defined within the pneumatic multiplexer 150 andare positioned to feed drug wells or ports 230 when the elongated neckof the fixed sensor probe 315 is fitted within with the sleeve 240. Thepneumatic multiplexer 150 serves to deliver compressed gas to aplurality of ports (see FIG. 6 a) from a single source that may becontrolled by an electrical or mechanical gas regulator or valving.Other types of pneumatic, mechanical or hydraulic pressure actuators maybe used. For example, the actuator may be a piston within a sleeve, asdescribed in U.S. Pat. No. 4,498,510 to Minshew et al., or a controlledgas supply as described in U.S. Pat. No. 4,461,328 to Kenney, or anyother suitable means for ejecting liquid test compound from the bottomof the port 230 using an extrinsic force.

The use of a pneumatic multiplexer may be preferable for the sake ofsimplification and reduction of the number of components that supplycompressed gas to the apparatus. The currently preferred pneumaticmultiplexer 150 is discussed in greater detail below.

Referring to FIG. 4, a region 210 of the cartridge 110 includes firstand second ports 230. In use, a test compound such as a drug, drugcandidate, toxin, etc. is added to the ports 230 of cartridge 110 beforebeginning an analysis using a pipettor or other means. The compoundtypically will be an aqueous solution of a known concentration. Inpreferred embodiments, it is held within each port despite the presenceof a small outlet at its bottom by surface tension. The dimensions ofthe port inhibit leakage from the bottom and from the top end (forming ameniscus that prevents leakage if the apparatus is turned on its side orupside down). The test compound may be released by, e.g., theapplication of pressurized air.

It may be desirable to operate the apparatus with test liquids that aredifficult to contain using capillary force due to their relatively lowviscosity or electrostatic properties. In this case, a frangiblemembrane or a fragile material, such as wax may be attached to cover thehole in the bottom of the port 230, such that an extrinsic force canbreach the membrane to eject the liquid at a desired time.

In the depicted embodiment, the submersible sleeve 240 is disposedbetween first and second ports 230. Sensors 250, e.g., fluorophores, aredisposed on surface 325 at the lower end of the sleeve. The submersiblesleeve 240 is configured to receive the sensor probe 170.

An array of integrated sensor sleeves and compound storage and deliveryports may be fabricated as a single assembly using a low costfabrication process such as injection molding so that the cartridge maybe disposed of after use.

Referring to FIG. 5, the well 220 is formed of, e.g., molded plastic,such as polystyrene or polypropylene. In use, cell media 500 and livecells 510 are disposed in the well 220. Cells 510 may or may not adhereto a bottom surface 520 of the well, and the bottom surface may betreated or coated to encourage adherence. Alternatively, cells may besuspended within the media.

Referring to FIGS. 6 a and 6 b, in use, when the parts are assembled,they allow simultaneous sensing of constituents in the cell media inplural wells simultaneously, and delivery of test compound from theports.

As illustrated, the fixed probe structure and drug loaded cartridge areassembled such that the outer tubing holding the fiber optic bundle isdisposed within the sleeve of the cartridge, and the assembly isreciprocated from an up position, where the probe tip and sensors aredisposed in the cell medium, to a lower, data gathering position,preferably one that reduces the volume of media about the cells so as toimprove the ability of the sensor to detect changes in the concentrationof an analyte in the media about the cells (see US 2005/0054028). In thepreferred embodiment, the sensors 250 disposed on the lower surface 325of the sensor sleeve 240 remains submerged during mixing, equilibrating,and measurement steps. One or more constituents within the mediasecreted from or absorbed by the cells may by analyzed. In a firstlowered position (FIG. 9 a), a fluid, such as a drug sample, isdelivered from one of the ports 230 to the cell medium, in thisembodiment impelled by air pressure communicated through air channels310. As noted above, the drug may be released through a small holedisposed at a bottom portion of the port 230.

After the fluid is dispensed into the media, the sensor sleeve 240 maybe raised and lowered one or more times while remaining submerged in themedia to mix the fluid with the media. The sensors 250 may remaindisposed within the media during the dispensing and mixing steps,thereby reducing stabilization periods.

After the test fluid is dispensed and mixed with the media, the sensors250 and sensor sleeve 240 are lowered to a second lower position in thewell 220. A bottom portion of the well 220 may include a seating surfacefor the sensor sleeve 240, e.g., an internal step defining a step planeabove a bottom plane of the well 220, the step plane and bottom planebeing parallel planes. In a microwell microplate, the height of the stepplane may generally be less than about 1 mm above the bottom plane andtypically less than about 50 μm to 200 μm above the bottom plane.Alternatively, a flat bottomed well or other well configuration may beused, and the fluorophore probes may disposed on surface 255 within arecess formed by a wall extending slightly beyond the surface asdisclosed above. In either case, in this embodiment a small volumesubchamber is formed about cells when the assembly is disposed in a downposition. Relatively small changes in the concentration of theconstituent than can be detected by the fluorophore probes, as themeasurement is taken within the confines of a much smaller volume ofmedium. This subvolume is maintained for a short time period to make ameasurement, and the assembly is moved upwardly, permitting the cells tobe exposed to the full well volume of its medium.

In an alternative embodiment, the test fluid from the port may bedelivered to the media when the sensor sleeve in the partially raised,but still submerged position.

During or after the delivery of the test fluid to the well, theconstituent in the medium may be analyzed to determine any changes, andthe measurements can be repeated with or without intermediate additionof test compounds. Any number of constituents of the media may beanalyzed, including dissolved gasses, ions, proteins, metabolicsubstrates, salts, and minerals. These constituents may be consumed bythe cells (such as O₂), or may be produced by the cells either as abyproduct (such as CO₂ and NH₃) or as a secreted factor (such asinsulin, cytokines, chemokines, hormones, or antibodies). Ions such asH⁺, Na⁺, K⁺, and Ca⁺⁺ secreted or extracted by cells in various cellularmetabolism processes may also be analyzed. Substrates either consumed orproduced by cells such as glucose, fatty acid, amino acids, glutamine,glycogen, and pyruvate may be analyzed. Specialized media may be used toimprove the sensitivity of the measurement. For example, a change in pHresulting from extracellular acidification can be increased by using amedia with reduced buffer capacity, such as bicarbonate-free media.

The method may be used to measure any number of attributes of cells andcellular function. For example, cell viability and metabolic rate may bedetermined from measurements of oxygen consumption rate, extracellularacidification rate, or other metabolic analyte fluxes. By comparison ofone or more analyte flux rates to a known rate per cell, cell number maybe determined and therefore growth rates can be monitored.

The introduction of an environment altering constituent such as achemical, dissolved gas, or nutrient may be applied to either the fullvolume of the well or alternatively to only the reduced volume of thewell. In the latter embodiment, the volume of media surrounding thecells is first reduced, the constituents of the media are measured, andthe volume is restored to its original value. The volume is then againreduced and the environment immediately surrounding the cells withinonly the reduced volume is then altered, by the addition of aconstituent from one of the four corresponding ports. This may beaccomplished by discharging the constituent from a port proximate thesensors or the bottom of the sleeve, for example. One or moremeasurements in the reduced volume are made in the presence of theconstituent. After this measurement cycle, the media within the reducedvolume may be exchanged one or more times to flush out the constituentbefore exposing cells once again to the full original volume. Thisapproach may provide a benefit of reducing the volume of compoundrequired. It may also provide the possibility of studying isolatedeffects without contaminating the entire volume, thereby, in effect,simulating a flow system in microplate format.

In preferred embodiments, as illustrated in the drawing, a plurality ofsensors are inserted and disposed simultaneously or sequentially in acorresponding plurality of wells in the multiwell plate, andconstituents related to respective cell cultures in respective wells areanalyzed. The respective constituents may include the same constituent.Respective test fluids may be delivered to the respective wells whilethe respective sensors remain in equilibrium with, preferably remaindisposed within the media in respective wells. It is possible tomaintain equilibrium with many sensors, particularly fluorophoresensors, while the sensor body is removed from the media for a shorttime, e.g., if the probe remains wetted, permitting maintenance ofequilibrium while adding test fluid. In one embodiment, the respectivetest fluids may be the same test fluid. The respective constituentsrelated to respective cells within media in respective wells may beanalyzed to determine any respective changes therein. These delivery andanalysis steps may be repeated. In another embodiment, the delivery stepis repeated with a different test fluid.

In some instances, the delivery and analysis may be repeated after atime period. More particularly, sequential measurements of a singlegroup of cells may be made at predetermined time intervals to analyzethe effect of a compound addition temporally, for example to examine theeffect of exposure to a drug, chemical, or toxin. In this method, thevolume of media surrounding the cells is first reduced, the constituentsof the media are measured, and the volume is restored to its originalvalue. The environment surrounding the cells is then altered, such as byadding one or more predetermined concentrations of a ligand thatactivates a transmembrane receptor, changing the dissolved oxygen level,or adding a nutrient. One or more additional measurement cycles then areperformed using the temporarily reduced volume method, to analyze theeffect of the altered extracellular environment.

Equilibration between the sensor and the media may be maintained duringthe delivery step. Thermal equilibrium may be substantially maintainedbetween the test fluid and media during the delivery.

Referring to FIGS. 7 and 8, the currently preferred form of themultiplexer 150 is shown. It comprises a laminated assembly of multiplelayers 700 of planar polymeric sheet material containing machinedchannels 710 for gas flow, sandwiched between a cover sheet 800 andcartridge facing gasket 810. One such arrangement uses four layers,e.g., four machined blocks placed in different orientations, to create apneumatic multiplexer enabling the dispensing of fluid from any one offour ports disposed in each region of the cartridge. The multiplexerenables the delivery of gas from a single gas inlet to multiple outlets.In use, the multiplexer is disposed between a pressure source and thecartridge, with the multiplexer adapted to be in fluidic communicationwith a plurality of ports formed in the cartridge. The multiplexer maybe selectively in fluidic communication with an exclusive set of portsformed in the cartridge.

Referring to FIG. 9, the sensor probe 170 is depicted submerged in theliquid media contained within a microplate well 220. The drug deliveryapparatus is shown activated using gas pressure from the pressurized gassupply 160 to deliver a drug from the port 230 to the media.

FIG. 10 schematically illustrate one embodiment of the inventionrealized as an instrument and software for analyzing cells undergoingvarious experimental processes using any of the techniques describedabove. A key element of the invention is a data file shared byinstrument operating system running on the embedded instrument computer,and desktop software running on a user's personal desktop computer.

As illustrated in FIG. 10, Desktop software 900 contains a userinterface that allows a user to enter experiment design information intodata file 901. Experiment design information may include the type ofcells, number of cells, type of drug, and concentration of drugcontained in each microplate well, the required measurement time, mediamixing time, the analyte to be assayed, or other data that defineattributes of the experiment to be run by the instrument.

Instrument operating system software 902 both receives experiment designinformation from, and stores experiment results to, data file 901.Operating system software 902 also contains a user interface for viewingand modification of experiment design information and for viewing ofexperiment results.

The instrument operating system software provides actuation and controlof motors, heaters and other devices based on the settings provided inthe data file. During each measurement cycle, measured data may bedisplayed on the user interface and concurrently added to the data file.At the end of a complete experiment, the data file, containingexperiment definition data, and measured sensor data, may be stored andtransmitted to the user's desktop computer for analysis. The user may athird-party analysis software package that draws data from the datafile. Examples of suitable third-party analysis software includeMICROSOFT EXCEL (Microsoft Corp), JMP (SAS Corp), and SIGMA PLOT (SystatCorp).

In a preferred embodiment, data file 901 is in the form of aspreadsheet.

In another preferred embodiment, data file 901 contains experimentdesign information and experiment results as separate worksheets withinone spreadsheet file.

In another preferred embodiment, data file 901 contains experimentdesign information, experiment results, and a data analysis tool, eachas separate worksheets within one spreadsheet file.

Data file 901 may be formatted as a workbook file for use within aspreadsheet software application such as Microsoft Excel.

Further, in a preferred embodiment of the data file, the experimentdefinition information and instrument-generated data may be duplicatedand additionally saved in machine-readable binary format on a separatehidden, password-protected area within the file. This capabilitypreserves the integrity of the original data while changes are made bythe user for analysis.

In another embodiment, proprietary binary data packets may be passeddirectly to other software configurations encoded with the customgraphical user interface and display areas. These alternative softwareenvironments might include traditional Windows or Macintoshapplications, stand-alone executable files with the embedded binarydata, web browser applications configured to load and display the data,or other viewing environments.

Referring to FIGS. 11 and 12, the system includes a graphicaluser-interface for accepting instructions relating to the experimentsand presenting results therefrom. Specifically, and in one embodiment,graphical user interface 1100 includes multiple display areas (e.g.,cells in a spreadsheet program in which each cell can be individuallyaddressed using row and column designators). Each display area may, forexample, represent one of the wells in a microplate, thus providing dataspecific to the cells in each well, and in some cases also includevarious parameters of the experiment and/or results of the experimentbased, for example, on signals received from the probes 170. Inembodiments in which multiple microplates are used simultaneously (orsubstantially simultaneously), inputs, parameters and/or results of theexperiments from the different wellplates may be presented usingmultiple spreadsheets, such as tabbed worksheets in EXCEL.

In some embodiments, the system also includes an analysis module forproducing graphical representations and/or statistical analysis of thedata acquired by the probes and presented within the user interface.Referring to FIG. 12, the results of the experiments, as well as theoutputs (both graphical and textual) can also be represented withinuser-interface 1200. For example, individual icons, images (e.g., GIFfiles, JPEG files) or colorations of display areas can be used torepresent the current (or most recently measured) pH of an assay, and agraphical display can be used to represent the same measurement (orothers) over time.

In a preferred embodiment, the results of an experiment may be presentedto the user in the form of a chart having data from each of two sensorsshown on each of two axes. For example, oxygen consumption rate may bedisplayed on the ordinate while extracellular acidification rate isshown on the abscissa. As shown in FIG. 12, chart 1210 displays datafrom each well of a multi-well experiment as a dot with an associatedlabel and error bar set.

EXAMPLES

The following examples illustrate certain exemplary and preferredembodiments and applications of the instant invention, but are notintended to be illustrative of all embodiments and applications.

Example 1 Evaluation of a 96 Well Drug Delivery Cartridge and PneumaticMultiplexer

Probes incorporating four drug wells or ports were fabricated frompolystyrene material using injection molding. Twenty four probes werethen bound together using an elastomeric sheet to form a single 4″×6″cartridge unit that is suitable for use as a disposable measurement anddrug delivery assembly. A pneumatic multiplexer was fabricated bymachining gas channels in four polystyrene blocks, then bonding theselayers together and applying a cover. The multiplexer was then clampedto the cartridge.

50 μl of water containing a colored dye was introduced to each of the 96drug wells using an automated pipetting system (Biotec 2000). A gas(air) accumulator was pressurized to 15 psi. Gas hoses were used tosupply air from the accumulator to four electrically actuated solenoidvalves. Each valve was mounted on the multiplexer, and the multiplexergas channels were arranged such that actuation of a single solenoidwould provide gas flow to 24 of the 96 drug wells.

The cartridge and multiplexer assembly was then placed above a 24 wellmicroplate reservoir (Innovative Microplate). An electrical drivecircuit was configured to actuate each solenoid for 250 μsec in order todeliver the fluid from the drug wells.

Upon first actuation of the solenoids, nearly complete delivery of waterwas observed in 20 of the 24 wells. The second, third and fourthsolenoid were then actuated, giving similar results.

A silicone rubber seal was then inserted between the multiplexer and thecartridge, and the experiment was repeated.

Complete injection of fluid from 24 wells was observed when the firstand second solenoid were actuated. Some residual water was seen inseveral wells actuated by the third and fourth solenoid.

The accumulator pressure was then reduced to 5 psi, and was rechargedbetween sequential actuation of solenoids one through four. Theelectronic circuit was then adjusted to increase the actuation time to275 μsec. In this case, complete injection of water was noted for eachof the 96 drug wells.

Example 2 Performance Measurement of a 96 Well Drug Delivery Cartridgeand Pneumatic Multiplexer

A test was performed using the components and method described inExample 1, except that a mixture of saline solution and Tartrazine wassubstituted for water in the drug wells. The fluid was injected into amicroplate reservoir, and then the absorbance of the contents of eachwell in the reservoir was measured using a Molecular Devices Versamaxmicroplate reader. Absorbance readings indirectly measure dye injectionvolume and demonstrate injection performance.

The experiment was performed with and without a flexible seal betweenthe multiplexer and cartridge, and three volumes of saline/Tartrazine(50, 75 and 100 μl) were injected. The resulting absorbance values areshown in Table E1.

TABLE E1 Absorbance measurements for injection of Tartrazine dye intowater using pneumatic multiplexer Injection Performance Test 1 InjectionPerformance Test 2 Column Column Row A B C D E F Row A B C D E F  50 uLTartrazine  50 uL Tartrazine 1 0.223 0.222 0.269 0.244 0.223 0.219 10.222 0.222 0.234 0.220 0.216 0.223 2 0.225 0.232 0.226 0.228 0.2210.229 2 0.221 0.225 0.223 0.226 0.226 0.223 3 0.225 0.216 0.219 0.2190.221 0.222 3 0.211 0.216 0.220 0.215 0.237 0.230 4 0.219 0.219 0.2210.248 0.223 0.222 4 0.222 0.222 0.225 0.223 0.221 0.223  75 uLTartrazine  75 uL Tartrazine 1 0.305 0.300 0.282 0.289 0.326 0.296 10.326 0.300 0.320 0.317 0.319 0.314 2 0.292 0.282 0.292 0.281 0.2850.292 2 0.311 0.309 0.310 0.310 0.314 0.308 3 0.277 0.279 0.274 0.2840.282 0.281 3 0.308 0.301 0.310 0.307 0.314 0.318 4 0.282 0.279 0.3290.282 0.284 0.293 4 0.308 0.308 0.313 0.319 0.317 0.307 100 uLTartrazine 100 uL Tartrazine 1 0.349 0.345 0.343 0.343 0.339 0.335 10.358 0.385 0.357 0.346 0.350 0.356 2 0.340 0.332 0.338 0.340 0.3430.342 2 0.365 0.343 0.359 0.348 0.353 0.357 3 0.342 0.342 0.336 0.3350.339 0.337 3 0.349 0.346 0.351 0.349 0.357 0.353 4 0.345 0.295 0.3450.344 0.355 0.348 4 0.358 0.349 0.357 0.355 0.353 0.352 Tartrazine MeanTartrazine Mean qty absorb Std Dev c.v. qty absorb Std Dev c.v.  50 ul0.23 0.0118 5.2%  50 ul 0.22 0.0056 2.5%  75 ul 0.29 0.0139 4.8%  75 ul0.31 0.0061 2.0% 100 ul 0.34 0.0108 3.2% 100 ul 0.35 0.0083 2.3%

Example 3 Metabolic Rate Assay Using a 96 Well Drug Delivery Cartridgeand Pneumatic Multiplexer

A test was performed using the components described in Example 1, and a24 well microplate containing 30×10³ HEP-G2 human hepatocellular livercarcinoma cells per well. Three initial “baseline” measurements ofcellular oxygen consumption rate (OCR) and extracellular acidificationrate (ECAR) were performed at eleven minute intervals using a 4 minutemeasurement period.

70 uL of FCCP, from one of the four injector ports, was then added toeach well containing 630 μL of media and cells using the methoddescribed in example #1, followed by measurement of OCR and ECAR. Thiswas repeated three additional times using the second, third and fourthinjector ports. Two control columns, A and F, were injected four timeswith vehicle only. Columns B, C, D and E contained three replicate wellsreceiving 4 injections of either a low (FIG. 13 a, aqua), medium-1 (FIG.13 b, orange), medium-2 (FIG. 13 c, pink) or high (FIG. 13 d, blue) doseseries of FCCP. The final concentration of FCCP in the well is shownabove each graph for each injection, A-D. The cumulative addition ofFCCP stock concentrations from each injector port followed bymeasurement of OCR and ECAR enabled a four-point dose curve to begenerated in each well.

FCCP induces mitochondrial uncoupling and causes cells to increase theirmetabolic rate and therefore OCR and ECAR. As demonstrated in FIG. 13,depending on the final concentration of FCCP, each series producedeither no or an increasingly higher OCR and ECAR response until toxicitywas reached as demonstrated in the high dose series (FIG. 13 d). Bymeasuring OCR and ECAR simultaneously the total metabolic rate andcapacity of the HepG2 cells could be determined. By being able tocumulatively add increasing concentrations of FCCP several dose curvescan be generated in a single assay while minimizing well-to-wellvariation inherent in all cell-based assays.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativeof the invention described herein. Various features and elements of thedifferent embodiments can be used in different combinations andpermutation, as will be apparent to those skilled in the art. Scope ofthe invention is thus indicated by the appended claims rather than bythe foregoing description, and all changes which come within the meaningand range of equivalency of the claims are therefore intended to beembraced herein.

What is claimed is:
 1. A cartridge which mates with a plate defining aplurality of wells, the cartridge comprising: a substantially planarelement comprising a plurality of regions corresponding to a number ofrespective openings of the wells in the plate, the regions being spacedapart so as to match a spacing of at least a portion of the multiplewells; located in plural respective regions of the cartridge, at leastone of a sensor to analyze a constituent in a well, and an aperture toreceive a sensor, and at least one port formed in the cartridge in atleast a subset of the regions, the port being adapted to deliver a testfluid to a respective well of the plate during the time said sensor isdisposed within liquid within said well.
 2. The cartridge of claim 1,wherein the port forms a capillary aperture to retain test fluid in theport absent an external force.
 3. The cartridge of claim 2, wherein theexternal force is selected from the group consisting of a positivepressure differential force, a negative pressure differential force, anda centrifugal force.
 4. The cartridge of claim 1, wherein the sensor iscompliantly attached to the planar element.
 5. The cartridge of claim 1,further comprising a second port formed in the cartridge in the at leastone region, the second port adapted to deliver a second test fluid tothe respective well.
 6. The cartridge of claim 1, wherein the cartridgeforms a cover for the multiwell plate to reduce at least one ofcontamination and evaporation of sample in the multiwell plate.
 7. Thecartridge of claim 1, further comprising, in multiple regions of thecartridge, at least one port and at least one of the sensor and anaperture adapted to receive the sensor.
 8. The cartridge of claim 7,wherein all of the ports are in fluidic communication.
 9. The cartridgeof claim 7, further comprising a second port formed in the cartridge inevery region.
 10. The cartridge of claim 9, wherein the second ports arein fluidic communication with each other and not in fluidiccommunication with other ports.
 11. The cartridge of claim 7 comprising24, 96, or 384 regions mated with 24, 96, or 384 well multiwell plates,each region comprising said sensor or a portion thereof or an apertureadapted to receive the sensor, and a set of 2, 3, 4, 5, 6, 7, or 8ports.
 12. The cartridge of claim 11, further comprising a multiplexerin fluidic communication with each set of ports.
 13. The cartridge ofclaim 12, wherein the multiplexer is adapted to connect to a singlepneumatic source to permit delivering fluid to the wells sequentiallyfrom each set of ports.
 14. The cartridge of claim 1 wherein the atleast one of the sensor or portion thereof adapted to analyze aconstituent in a well and the aperture adapted to receive the sensorcomprises a sensor sleeve structure having a light translucent surfaceand disposed thereon a fluorophore having fluorescent propertiesdependent on at least one of the presence and the concentration of aconstituent in the well.
 15. The cartridge of claim 14 wherein thesensor sleeve further comprises an elongate housing to receive a waveguide for at least one of stimulating the fluorophore and receivingfluorescent emissions from the fluorophore.